The present invention relates to high resolution cryosurgical method and apparatus which enable to effectively and accurately freeze and thereby destroy a predetermined portion of a tissue while minimizing damage to adjacent tissues and organs.
Cryosurgical procedures involve deep tissue freezing which results in tissue destruction due to rupture of cells and or cell organelles within the tissue. Deep tissue freezing is effected by insertion of a tip of a cryosurgical device into the tissue, either endoscopically or laparoscopically, and a formation of, what is known in the art as, an ice-ball around the tip.
In order to effectively destroy a tissue by such an ice-ball, the diameter of the ball should be substantially larger than the region of the tissue to be treated, which constraint derives from the specific profile of temperature distribution across the ice-ball.
Specifically, the temperature required for effectively destroying a tissue is about -40.degree. C. or cooler. However, the temperature at the surface of the ice-ball is 0.degree. C. The temperature declines exponentially towards the center of the ball such that an isothermal surface of about -40.degree. C. is typically located within the ice-ball substantially at the half way between the center of the ball and its surface.
Thus, in order to effectively destroy a tissue there is a need to locate the isothermal surface of -40.degree. C. at the periphery of the treated tissue, thereby exposing adjacent, usually healthy, tissues to the external portions of the ice-ball. The application of temperatures of between about -40.degree. C. and 0.degree. C. to such healthy tissues usually causes substantial damage thereto, which damage may result in temporary or permanent impairment of functional organs.
In addition, should the adjacent tissues are present at opposite borders with respect to the freeze treated tissue, such as in the case of prostate freeze treatments, as further detailed below, and since the growth of the ice-ball is in substantially similar rate in all directions toward its periphery, if the tip of the cryosurgical device is not precisely centered, the ice-ball reaches one of the borders before it reaches the other border, and decision making of whether to continue the process of freezing, risking a damage to close healthy tissues, or to halt the process of freezing, risking a non-complete destruction of the treated tissue, must be made.
Although the present invention is applicable to any cryosurgical treatment, discussion is hereinafter focused on a cryosurgical treatment of a patient's prostate.
Thus, when treating a tumor located at a patient's prostate, there is a trade-of between two options: (a) effectively destroying the prostatic tissue extending between the prostatic urethra and the periphery of the prostate and causing unavoidable damage to the patient's urethra or organs adjacent the prostate such as the rectum and nerves; (b) avoiding the damaging of the prostatic urethra and adjacent organs, but exposing the patient to the risk of malignancy due to ineffective destruction of the prostate tumor.
Currently, cryosurgery procedures for treating the prostate include the introduction of 5-7 probes into the prostate, the probes being typically arranged around the prostatic urethra such that a single probe is located, preferably centered, between the prostatic urethra and the periphery of the prostate. The dimensions of such a single probe are usually adapted for effectively treating the prostatic tissue segment extending from the urethra to the periphery of the prostate, e.g., a tip of 3 millimeters in diameter, generating an ice-ball of 3-4 centimeters in diameter, depending on the size of the prostate. Since a single ice-ball is used for freezing such a prostatic tissue segment, the volume of adjacent tissues exposed to damage is substantially greater than the volume of the treated tissue. For example, if the area of the ice-ball in cross section is .pi.R.sup.2, and an effective treatment of at least -40.degree. C. is provided to an area of .pi.(R/2).sup.2 (in cross section), then the area of adjacent tissues (in cross section) exposed to between about -40.degree. C. and about 0.degree. C. is .pi.R.sup.2 -0.25(.pi.R.sup.2)=0.75(.pi.R.sup.2), which is three times the area of the tissue effectively treated by the ice-ball.
The current strategy used for avoiding excessive damage to adjacent tissues is to use such a single probe of a smaller diameter producing an ice-ball of smaller size, thereby exposing the patient to the danger of malignancy.
Thus, the prior art methods and devices fail to provide effective resolution of treatment along the planes perpendicular to the axis of penetration of the cryosurgical probe into the patient's organ.
Furthermore, since anatomical organs such as the prostate usually feature an asymmetric three dimensional shape, the introduction of a cryosurgical probe along a specific path of penetration within the organ may provide effective treatment to specific regions located at specific depths of penetration but at the same time may severely damage other portions of the organ located at other depths of penetration.
There is thus a widely recognized need for, and it would be highly advantageous to have, cryosurgical method and device which provide high resolution of treatment along the axis of penetration of the cryosurgical probe into the patient's organ as well as along the planes perpendicular to the axis of penetration.
Specifically, there is a widely recognized need for, and it would be highly advantageous to have, high resolution cryosurgical method and device which enable to effectively destroy selective portions of a patient's tissue while minimizing damage to adjacent tissues and organs.
Furthermore, there is a widely recognized need for such method and device which enable to selectively treat various portions of the tissue located at different depths of the organ, thereby effectively freezing selected portions of the tissue while avoiding the damaging of other tissues and organs located at other depth along the axis of penetration.
It would be further advantageous to have such cryosurgical method and device which three dimensionally map an organ of a patient so as to form a three dimensional grid thereof, and which apply a multi-probe system introduced into the organ according to the grid so as to enable systematic high-resolution three dimensional cryosurgical treatment of the organ and selectively destroy the treated tissue with minimal damage to surrounding, healthy, tissues.